I'd agree for bipolar... For MOSFET H-bridges all-n-channel is common however, but special circuitry is in place to generate gate voltageshigher than the supply for the top MOSFETS.

Here's a bipolar H-bridge suggestion:The middle resistors (R5 and R6) are used to set the maximum base current to the switch transistors,so their value depends on the supply voltage and desired output current (and current gain of theswitch transistors).

This actual circuit I've used with surface mount NPN/PNP superbeta transistor pairs for the switches, whichhave very low Vsat, and a clever trick of using a small surface mount bridge rectifier to provide all 4free-wheeling diodes in one go.

You must be careful not to drive both inputs high at the same time! Some means of monitoring over-currentwould be a wise addition.

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juanps90

Fine, but how does that make any difference? Can I build my own h bridge using 4 IRF520? Maybe using two of these and two transistors?

It appears that an h bridge can be built because I actually have done so, the problem is that there is a considerable voltage drop that would cause heat and energy waste so it definitely is not the way to go.

Can I build my own h bridge using 4 IRF520? Maybe using two of these and two transistors?

I think h-bridges using all NPN MOSFETs use a bootstrap circuit to keep the upstream MOSFET gate voltage higher than the h-bridge supply voltage. If you are thinking of making a DIY MOSFET h-bridge, then the below discussion might be of interest to you. Lots of inexpensive h-bridges now on ebay.

http://arduino.cc/forum/index.php?topic=53425.0

Google forum search: Use Google Search box in upper right side of this page. Why I like my 2005 Rio Yellow Honda S2000 https://www.youtube.com/watch?v=pWjMvrkUqX0

Note that that bootstrap circuit imposes two restrictions on the H-bridge:

1) When top MOSFET is idle (off) you should turn on the lower MOSFET to keep the capacitor charged (in the diagram the load resistor is performing that role).2) The PWM duty cycle of the upper MOSFET must not reach 100% - in fact you have to ensure the off-periods are long enough for the capacitor to recharge through the diode and lower MOSFET, and that the on-periods are short enough that the capacitor doesn't self-discharge through leakage currents. You need to keep the capacitor C charged all the time.

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